{"gene":"FDX2","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2010,"finding":"FDX2 (ferredoxin 2) is essential for heme A and Fe/S cluster biosynthesis in human mitochondria, while its paralog FDX1 is specific for steroidogenesis. FDX2 deficiency caused impaired Fe/S protein biogenesis, leading to increased cellular iron uptake and mitochondrial iron accumulation. FDX1 was unable to efficiently reduce mitochondrial cytochromes P450 or replace FDX2 function in Fe/S cluster assembly, demonstrating distinct substrate specificity.","method":"RNAi depletion of FDX1 and FDX2 in human cells with measurement of heme A, Fe/S cluster assembly, steroid biosynthesis, and iron homeostasis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean RNAi knockdown with multiple orthogonal biochemical readouts, replicated across both isoforms, highly cited foundational study","pmids":["20547883"],"is_preprint":false},{"year":2017,"finding":"Both FDX1 and FDX2 bind the cysteine desulfurase complex (NFS1/ISD11/ACP) via residues near their Fe-S clusters; FDX2 binds the complex more tightly than FDX1 and supports faster in vitro Fe/S cluster assembly on ISCU. Both ferredoxins donate electrons to the cysteine desulfurase complex, converting L-cysteine to L-alanine and sulfide.","method":"NMR spectroscopy mapping of binding interfaces, isothermal titration calorimetry, in vitro Fe/S cluster assembly assay on ISCU","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro system with NMR, ITC, and functional assembly assay in single study","pmids":["28001042"],"is_preprint":false},{"year":2020,"finding":"FDX2, together with its reductase FDXR, provides electrons that catalyze reductive [2Fe-2S] cluster fusion on the ISCA1-ISCA2 scaffold in an IBA57-dependent fashion, enabling maturation of mitochondrial [4Fe-4S] proteins such as aconitase. FDX1 and other cellular reducing systems cannot substitute for FDX2 in this reaction.","method":"In vitro reconstitution of [4Fe-4S] aconitase maturation without artificial reductants, using purified GLRX5 as cluster donor and all ISC components","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — full reconstitution with all physiological components, specificity demonstrated by FDX1 substitution failure","pmids":["32817474"],"is_preprint":false},{"year":2022,"finding":"FDX2 is exclusively involved in Fe/S protein maturation (both [2Fe-2S] and [4Fe-4S] clusters), while FDX1 is specific for steroidogenesis, heme a biosynthesis, and lipoyl cofactor biosynthesis (providing electrons for lipoyl synthase radical chain reaction). The distinct target specificity of each ferredoxin was mapped to small conserved sequence motifs; swapping these motifs transferred target specificity between the two isoforms.","method":"RNAi knockdown, in vitro electron transfer assays, sequence motif swapping mutagenesis, biochemical pathway activity measurements","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including mutagenesis that directly transfers function, replicated across pathways, highly cited","pmids":["36280795"],"is_preprint":false},{"year":2013,"finding":"Loss-of-function mutation in FDX2 (c.1A>T disrupting ATG start codon) causes severely impaired activities of Fe/S-dependent respiratory chain complexes I, II, III and mitochondrial aconitase, establishing FDX2 as the second component of the Fe/S cluster biogenesis machinery after ISCU.","method":"Exome sequencing with homozygosity mapping; enzyme activity assays of respiratory chain complexes in patient skeletal muscle; western blot confirming protein loss","journal":"European journal of human genetics : EJHG","confidence":"Medium","confidence_rationale":"Tier 2 — patient loss-of-function with multiple biochemical readouts confirming Fe/S pathway defect","pmids":["24281368"],"is_preprint":false},{"year":2024,"finding":"The pathogenic P144L mutation in FDX2 negatively affects the FDXR-dependent electron transfer pathway from NADPH to FDX2, reducing FDX2's capacity to assemble both [2Fe-2S] and [4Fe-4S] clusters. The C-terminal tail of FDX2 plays a functional role in electron transfer between FDX2 and FDXR. The P144L substitution alters protein-protein recognition between FDX2 and FDXR without perturbing the [2Fe-2S] cluster or overall protein structure.","method":"NMR structural and dynamic analysis of WT vs. P144L FDX2; in vitro electron transfer assays with FDXR; protein-protein interaction mapping","journal":"Protein science : a publication of the Protein Society","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal biophysical methods (NMR, in vitro electron transfer) with direct functional validation of mutant","pmids":["39467201"],"is_preprint":false},{"year":2025,"finding":"FDX2 and frataxin compete for occupancy at the same binding site on NFS1 (cysteine desulfurase). Excess FDX2 inhibits frataxin-stimulated NFS1 activity in vitro and blocks Fe/S cluster synthesis in mammalian cell culture. Dominant suppressor mutations at the FDX2-NFS1 binding interface boost Fe/S cluster levels in the absence of frataxin, and partial knockdown of FDX2 ameliorates frataxin-deficient phenotypes.","method":"Genome-scale forward genetic screen in C. elegans; in vitro NFS1 activity assays with FDX2 titration; mammalian cell culture Fe/S cluster synthesis assays; mouse model of Friedreich's ataxia with FDX2 heterozygous reduction","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — genetic screen validated by in vitro biochemistry and mammalian cell and mouse model experiments, multiple orthogonal approaches","pmids":["41372402"],"is_preprint":false},{"year":2024,"finding":"Conditional knockout of FDX2 in ovarian cancer cells causes global downregulation of Fe/S-containing proteins and Fe2+ overload, leading to DNA damage and p53 pathway activation. Depending on p53 status and phospholipid homeostasis, FDX2 loss drives either cellular senescence, apoptosis, or ferroptosis.","method":"Conditional knockout cell line; western blot for Fe/S proteins; Fe2+ measurement; DNA damage markers; p53 pathway analysis; ferroptosis sensitivity assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — clean conditional KO with multiple pathway readouts in single lab study","pmids":["39151727"],"is_preprint":false},{"year":2025,"finding":"A novel splicing mutation in FDX2 (c.200+4 A>G) generates a mutant protein with 19 N-terminal residues replaced by 21 different amino acids; patient cells have low FDX2 levels, impaired mitochondrial respiration, defects in Fe/S proteins, enhanced mitochondrial iron accumulation, and diminished mitochondrial SOD2 levels.","method":"Patient fibroblast analysis; NMR structural comparison of mutant vs. WT FDX2; mitochondrial respiration assays; Fe/S protein activity measurements; iron quantification","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — patient-derived cells with multiple biochemical readouts and structural characterization of mutant protein","pmids":["41372147"],"is_preprint":false},{"year":2025,"finding":"Paramagnetic NMR and DFT calculations reveal that the [Fe2S2]2+ cluster of FDX2 has inequivalent iron centers, with electron spin density transfer between inorganic sulfide ions and aliphatic carbon atoms via C-H---S-Fe3+ interactions; the magnetic exchange coupling constant between the two Fe3+ ions is ~386 cm-1.","method":"Paramagnetic NMR spectroscopy with complete assignment of binding-loop residues; density functional theory quantum chemical calculations","journal":"Inorganic chemistry","confidence":"Medium","confidence_rationale":"Tier 1 — structural/electronic characterization by NMR and DFT in single study without functional mutagenesis validation","pmids":["40121555"],"is_preprint":false}],"current_model":"FDX2 is a mitochondrial [2Fe-2S] ferredoxin that receives electrons from NADPH via FDXR and donates them specifically to the Fe/S cluster assembly machinery: it reduces the NFS1/ISD11/ACP cysteine desulfurase complex to drive [2Fe-2S] cluster synthesis on ISCU2, and subsequently catalyzes reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 (with IBA57) to form [4Fe-4S] clusters for mitochondrial [4Fe-4S] apoproteins; FDX2 and frataxin compete for the same site on NFS1, such that their stoichiometric balance regulates Fe/S cluster output, and FDX2's distinct substrate specificity (versus FDX1's role in steroidogenesis/heme a/lipoylation) is encoded by small conserved sequence motifs."},"narrative":{"teleology":[{"year":2010,"claim":"The first functional dichotomy between the two human ferredoxins was established: FDX2 is essential for Fe/S cluster and heme A biosynthesis while FDX1 is specific for steroidogenesis, resolving a long-standing question about why mammals retain two mitochondrial ferredoxins.","evidence":"RNAi depletion of FDX1 and FDX2 in human cells with measurement of multiple mitochondrial pathways","pmids":["20547883"],"confidence":"High","gaps":["No reconstituted biochemical system to show direct electron transfer to Fe/S assembly machinery","Heme A involvement of FDX2 was later reassigned to FDX1","Molecular basis of substrate selectivity between the two paralogs unknown"]},{"year":2013,"claim":"A human loss-of-function mutation confirmed FDX2's physiological essentiality for Fe/S-dependent mitochondrial enzymes and established FDX2 deficiency as a cause of mitochondrial disease.","evidence":"Exome sequencing identifying c.1A>T start-codon mutation; respiratory chain enzyme assays in patient muscle","pmids":["24281368"],"confidence":"Medium","gaps":["Single family; no rescue experiment to confirm causality","Degree of residual FDX2 protein expression not quantified precisely","No structure-function insight from this mutation"]},{"year":2017,"claim":"The physical interaction between FDX2 and the NFS1/ISD11/ACP cysteine desulfurase complex was mapped at atomic resolution, revealing that FDX2 binds more tightly than FDX1 and supports faster Fe/S cluster assembly on ISCU.","evidence":"NMR binding-interface mapping, isothermal titration calorimetry, and in vitro Fe/S cluster assembly on ISCU","pmids":["28001042"],"confidence":"High","gaps":["Binding interface of FDX2 with downstream late-acting ISC components not characterized","Physiological relevance of the affinity difference between FDX1 and FDX2 for the desulfurase complex not tested in cells"]},{"year":2020,"claim":"FDX2 was shown to be uniquely required for the late step of [4Fe-4S] cluster maturation, catalyzing reductive [2Fe-2S] cluster fusion on the ISCA1-ISCA2 scaffold in an IBA57-dependent manner — a reaction no other cellular reductant could support.","evidence":"Full in vitro reconstitution of [4Fe-4S] aconitase maturation with all physiological ISC components","pmids":["32817474"],"confidence":"High","gaps":["Structural basis of FDX2 recognition by the ISCA1-ISCA2 scaffold not determined","Whether FDX2 transfers one or two electrons per fusion event unclear"]},{"year":2022,"claim":"The molecular determinants encoding ferredoxin substrate specificity were identified: small conserved sequence motifs can transfer FDX2's Fe/S assembly role to FDX1 and vice versa, definitively separating the two paralogs' functions.","evidence":"Motif-swapping mutagenesis combined with RNAi knockdown and in vitro electron transfer assays","pmids":["36280795"],"confidence":"High","gaps":["Crystal or cryo-EM structure of the FDX2–target complex showing how these motifs mediate recognition unavailable","Whether the motifs affect binding affinity, electron transfer rate, or both was not quantitatively dissected"]},{"year":2024,"claim":"The pathogenic P144L mutation was shown to impair FDXR-dependent electron delivery to FDX2 by disrupting protein-protein recognition at FDX2's C-terminal tail without perturbing the [2Fe-2S] cluster, revealing a functional role for the C-terminus in the electron transfer relay.","evidence":"NMR structural/dynamic comparison of WT vs. P144L FDX2; in vitro electron transfer assays with FDXR","pmids":["39467201"],"confidence":"High","gaps":["Quantitative impact of P144L on in-cell Fe/S cluster levels not measured","Whether other disease mutations similarly target the FDXR interface unknown"]},{"year":2024,"claim":"Conditional FDX2 knockout in cancer cells revealed that global Fe/S protein loss triggers Fe²⁺ overload, DNA damage, and p53 activation, with cell fate (senescence, apoptosis, or ferroptosis) determined by p53 status and lipid homeostasis.","evidence":"Conditional KO in ovarian cancer cells; Fe²⁺ quantification; DNA damage markers; ferroptosis sensitivity assays","pmids":["39151727"],"confidence":"Medium","gaps":["Single cancer cell type; generalizability to other tissues not established","Whether ferroptosis sensitivity is a direct consequence of Fe/S loss or secondary iron overload not distinguished"]},{"year":2025,"claim":"A forward genetic screen uncovered that FDX2 and frataxin compete for the same binding site on NFS1, establishing that their stoichiometric balance directly regulates Fe/S cluster output and providing a mechanistic basis for therapeutic reduction of FDX2 in Friedreich's ataxia.","evidence":"Genome-scale C. elegans screen; in vitro NFS1 activity titrations; mammalian cell Fe/S assays; mouse Friedreich's ataxia model with FDX2 heterozygous reduction","pmids":["41372402"],"confidence":"High","gaps":["Structural basis of competitive binding at the shared NFS1 site not resolved at atomic level","Long-term safety and efficacy of FDX2 reduction in mammalian Friedreich's ataxia models not determined","Whether FDX2-frataxin competition is regulated by post-translational modifications unknown"]},{"year":2025,"claim":"Paramagnetic NMR combined with DFT calculations resolved the electronic structure of FDX2's [2Fe-2S]²⁺ cluster, revealing inequivalent iron centers and spin-density transfer through C-H···S-Fe³⁺ interactions.","evidence":"Paramagnetic NMR with full binding-loop assignment; DFT quantum chemical calculations","pmids":["40121555"],"confidence":"Medium","gaps":["No functional mutagenesis to test how perturbing these electronic features affects electron transfer","Whether these electronic properties differ between FDX2 and FDX1 and account for specificity not examined"]},{"year":null,"claim":"Key unresolved questions include the atomic-resolution structure of FDX2 in complex with NFS1 or ISCA1-ISCA2, the mechanism by which FDX2-frataxin competition is physiologically regulated, and whether FDX2 reduction is a viable therapeutic strategy for Friedreich's ataxia in long-term preclinical models.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of FDX2 bound to any of its physiological partner complexes","Regulatory mechanisms controlling FDX2 expression or stability in response to Fe/S demand unknown","Therapeutic window for FDX2 reduction in Friedreich's ataxia not defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,1,2,3,5]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,2,4,8]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,2,3,4]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[4,5,8]}],"complexes":[],"partners":["FDXR","NFS1","ISCU","ISCA1","ISCA2","IBA57","FXN"],"other_free_text":[]},"mechanistic_narrative":"FDX2 is a mitochondrial [2Fe-2S] ferredoxin dedicated to iron-sulfur cluster biogenesis. It accepts electrons from NADPH via ferredoxin reductase FDXR and donates them to the NFS1/ISD11/ACP cysteine desulfurase complex to drive [2Fe-2S] cluster assembly on ISCU2, and subsequently catalyzes reductive [2Fe-2S] cluster fusion on the ISCA1-ISCA2 scaffold (with IBA57) to generate [4Fe-4S] clusters for mitochondrial apoproteins; its paralog FDX1 cannot substitute in these reactions, and the distinct substrate specificity is encoded by small conserved sequence motifs [PMID:20547883, PMID:32817474, PMID:36280795]. FDX2 and frataxin compete for the same binding site on NFS1, and their stoichiometric balance governs Fe/S cluster output such that excess FDX2 inhibits frataxin-stimulated desulfurase activity and partial FDX2 reduction ameliorates frataxin-deficient phenotypes [PMID:41372402]. Loss-of-function mutations in FDX2 cause a mitochondrial disorder with impaired respiratory chain complex activities, mitochondrial iron accumulation, and myopathy [PMID:24281368, PMID:41372147]."},"prefetch_data":{"uniprot":{"accession":"Q6P4F2","full_name":"Ferredoxin-2, mitochondrial","aliases":["Adrenodoxin-like protein","Ferredoxin-1-like protein"],"length_aa":183,"mass_kda":19.5,"function":"Electron donor, of the core iron-sulfur cluster (ISC) assembly complex, that acts to reduce the persulfide into sulfide during [2Fe-2S] clusters assembly on the scaffolding protein ISCU (PubMed:28001042). The core iron-sulfur cluster (ISC) assembly complex is involved in the de novo synthesis of a [2Fe-2S] cluster, the first step of the mitochondrial iron-sulfur protein biogenesis (By similarity). This process is initiated by the cysteine desulfurase complex (NFS1:LYRM4:NDUFAB1) that produces persulfide which is delivered on the scaffold protein ISCU in a FXN-dependent manner (By similarity). Then this complex is stabilized by FDX2 which provides reducing equivalents to accomplish the [2Fe-2S] cluster assembly (By similarity). Finally, the [2Fe-2S] cluster is transferred from ISCU to chaperone proteins, including HSCB, HSPA9 and GLRX5 (By similarity). Essential for coenzyme Q biosynthesis: together with FDXR, transfers the electrons required for the hydroxylation reaction performed by COQ6 (PubMed:38425362)","subcellular_location":"Mitochondrion; Mitochondrion matrix","url":"https://www.uniprot.org/uniprotkb/Q6P4F2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/FDX2","classification":"Common Essential","n_dependent_lines":868,"n_total_lines":1208,"dependency_fraction":0.7185430463576159},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FDX2","total_profiled":1310},"omim":[{"mim_id":"614585","title":"FERREDOXIN 2; FDX2","url":"https://www.omim.org/entry/614585"},{"mim_id":"605711","title":"MULTIPLE MITOCHONDRIAL DYSFUNCTIONS SYNDROME 1; MMDS1","url":"https://www.omim.org/entry/605711"},{"mim_id":"251900","title":"MITOCHONDRIAL MYOPATHY, EPISODIC, WITH OR WITHOUT OPTIC ATROPHY AND REVERSIBLE LEUKOENCEPHALOPATHY; MEOAL","url":"https://www.omim.org/entry/251900"},{"mim_id":"103270","title":"FERREDOXIN REDUCTASE; FDXR","url":"https://www.omim.org/entry/103270"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FDX2"},"hgnc":{"alias_symbol":["MGC19604"],"prev_symbol":["FDX1L"]},"alphafold":{"accession":"Q6P4F2","domains":[{"cath_id":"3.10.20.30","chopping":"71-169","consensus_level":"high","plddt":93.3441,"start":71,"end":169}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6P4F2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6P4F2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6P4F2-F1-predicted_aligned_error_v6.png","plddt_mean":76.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FDX2","jax_strain_url":"https://www.jax.org/strain/search?query=FDX2"},"sequence":{"accession":"Q6P4F2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6P4F2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6P4F2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6P4F2"}},"corpus_meta":[{"pmid":"20547883","id":"PMC_20547883","title":"Humans possess two mitochondrial ferredoxins, Fdx1 and Fdx2, with distinct roles in steroidogenesis, heme, and Fe/S cluster biosynthesis.","date":"2010","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/20547883","citation_count":318,"is_preprint":false},{"pmid":"36280795","id":"PMC_36280795","title":"Functional spectrum and specificity of mitochondrial ferredoxins FDX1 and FDX2.","date":"2022","source":"Nature chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/36280795","citation_count":123,"is_preprint":false},{"pmid":"28001042","id":"PMC_28001042","title":"Human Mitochondrial Ferredoxin 1 (FDX1) and Ferredoxin 2 (FDX2) Both Bind Cysteine Desulfurase and Donate Electrons for Iron-Sulfur Cluster Biosynthesis.","date":"2017","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28001042","citation_count":116,"is_preprint":false},{"pmid":"24281368","id":"PMC_24281368","title":"Deleterious mutation in FDX1L gene is associated with a novel mitochondrial muscle myopathy.","date":"2013","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/24281368","citation_count":70,"is_preprint":false},{"pmid":"32817474","id":"PMC_32817474","title":"Mitochondrial [4Fe-4S] protein assembly involves reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 by electron flow from ferredoxin FDX2.","date":"2020","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/32817474","citation_count":69,"is_preprint":false},{"pmid":"30010796","id":"PMC_30010796","title":"A novel complex neurological phenotype due to a homozygous mutation in FDX2.","date":"2018","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/30010796","citation_count":40,"is_preprint":false},{"pmid":"26526668","id":"PMC_26526668","title":"Crystal structure and biochemical characterization of Chlamydomonas FDX2 reveal two residues that, when mutated, partially confer FDX2 the redox potential and catalytic properties of FDX1.","date":"2015","source":"Photosynthesis research","url":"https://pubmed.ncbi.nlm.nih.gov/26526668","citation_count":17,"is_preprint":false},{"pmid":"35079622","id":"PMC_35079622","title":"FDX2 and ISCU Gene Variations Lead to Rhabdomyolysis With Distinct Severity and Iron Regulation.","date":"2022","source":"Neurology. Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35079622","citation_count":15,"is_preprint":false},{"pmid":"39151727","id":"PMC_39151727","title":"FDX2, an iron-sulfur cluster assembly factor, is essential to prevent cellular senescence, apoptosis or ferroptosis of ovarian cancer cells.","date":"2024","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39151727","citation_count":12,"is_preprint":false},{"pmid":"39467201","id":"PMC_39467201","title":"Unraveling the molecular determinants of a rare human mitochondrial disorder caused by the P144L mutation of FDX2.","date":"2024","source":"Protein science : a publication of the Protein Society","url":"https://pubmed.ncbi.nlm.nih.gov/39467201","citation_count":8,"is_preprint":false},{"pmid":"34905296","id":"PMC_34905296","title":"Rare presentation of FDX2-related disorder and untargeted global metabolomics findings.","date":"2021","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/34905296","citation_count":7,"is_preprint":false},{"pmid":"38444577","id":"PMC_38444577","title":"Clinical, biochemical and molecular characterization of a new case with FDX2-related mitochondrial disorder: Potential biomarkers and treatment options.","date":"2024","source":"JIMD reports","url":"https://pubmed.ncbi.nlm.nih.gov/38444577","citation_count":6,"is_preprint":false},{"pmid":"37565517","id":"PMC_37565517","title":"Α rare case of myopathy, lactic acidosis, and severe rhabdomyolysis, due to a homozygous mutation of the ferredoxin-2 (FDX2) gene.","date":"2023","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/37565517","citation_count":5,"is_preprint":false},{"pmid":"40121555","id":"PMC_40121555","title":"Shedding Light on the Electron Delocalization Pathway at the [Fe2S2]2+ Cluster of FDX2.","date":"2025","source":"Inorganic chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/40121555","citation_count":3,"is_preprint":false},{"pmid":"41372402","id":"PMC_41372402","title":"Mutations in mitochondrial ferredoxin FDX2 suppress frataxin deficiency.","date":"2025","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/41372402","citation_count":2,"is_preprint":false},{"pmid":"41648530","id":"PMC_41648530","title":"Client distribution between Chlamydomonas FDX1 and FDX2 in carbon, nitrogen and sulfur assimilation.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41648530","citation_count":1,"is_preprint":false},{"pmid":"41372147","id":"PMC_41372147","title":"A novel mutation in FDX2 provides insights into the pathogenesis of MEOAL mitochondrial neuromuscular disease.","date":"2025","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/41372147","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.06.09.658195","title":"Placental Iron Utilisation in Fetal Growth Restriction: Alterations in Mitochondrial Heme Synthesis and Iron-Sulfur Cluster Assembly Pathways","date":"2025-06-12","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.09.658195","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11052,"output_tokens":2781,"usd":0.037435},"stage2":{"model":"claude-opus-4-6","input_tokens":6088,"output_tokens":2678,"usd":0.146085},"total_usd":0.18352,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"FDX2 (ferredoxin 2) is essential for heme A and Fe/S cluster biosynthesis in human mitochondria, while its paralog FDX1 is specific for steroidogenesis. FDX2 deficiency caused impaired Fe/S protein biogenesis, leading to increased cellular iron uptake and mitochondrial iron accumulation. FDX1 was unable to efficiently reduce mitochondrial cytochromes P450 or replace FDX2 function in Fe/S cluster assembly, demonstrating distinct substrate specificity.\",\n      \"method\": \"RNAi depletion of FDX1 and FDX2 in human cells with measurement of heme A, Fe/S cluster assembly, steroid biosynthesis, and iron homeostasis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean RNAi knockdown with multiple orthogonal biochemical readouts, replicated across both isoforms, highly cited foundational study\",\n      \"pmids\": [\"20547883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Both FDX1 and FDX2 bind the cysteine desulfurase complex (NFS1/ISD11/ACP) via residues near their Fe-S clusters; FDX2 binds the complex more tightly than FDX1 and supports faster in vitro Fe/S cluster assembly on ISCU. Both ferredoxins donate electrons to the cysteine desulfurase complex, converting L-cysteine to L-alanine and sulfide.\",\n      \"method\": \"NMR spectroscopy mapping of binding interfaces, isothermal titration calorimetry, in vitro Fe/S cluster assembly assay on ISCU\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro system with NMR, ITC, and functional assembly assay in single study\",\n      \"pmids\": [\"28001042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FDX2, together with its reductase FDXR, provides electrons that catalyze reductive [2Fe-2S] cluster fusion on the ISCA1-ISCA2 scaffold in an IBA57-dependent fashion, enabling maturation of mitochondrial [4Fe-4S] proteins such as aconitase. FDX1 and other cellular reducing systems cannot substitute for FDX2 in this reaction.\",\n      \"method\": \"In vitro reconstitution of [4Fe-4S] aconitase maturation without artificial reductants, using purified GLRX5 as cluster donor and all ISC components\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — full reconstitution with all physiological components, specificity demonstrated by FDX1 substitution failure\",\n      \"pmids\": [\"32817474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FDX2 is exclusively involved in Fe/S protein maturation (both [2Fe-2S] and [4Fe-4S] clusters), while FDX1 is specific for steroidogenesis, heme a biosynthesis, and lipoyl cofactor biosynthesis (providing electrons for lipoyl synthase radical chain reaction). The distinct target specificity of each ferredoxin was mapped to small conserved sequence motifs; swapping these motifs transferred target specificity between the two isoforms.\",\n      \"method\": \"RNAi knockdown, in vitro electron transfer assays, sequence motif swapping mutagenesis, biochemical pathway activity measurements\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including mutagenesis that directly transfers function, replicated across pathways, highly cited\",\n      \"pmids\": [\"36280795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Loss-of-function mutation in FDX2 (c.1A>T disrupting ATG start codon) causes severely impaired activities of Fe/S-dependent respiratory chain complexes I, II, III and mitochondrial aconitase, establishing FDX2 as the second component of the Fe/S cluster biogenesis machinery after ISCU.\",\n      \"method\": \"Exome sequencing with homozygosity mapping; enzyme activity assays of respiratory chain complexes in patient skeletal muscle; western blot confirming protein loss\",\n      \"journal\": \"European journal of human genetics : EJHG\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient loss-of-function with multiple biochemical readouts confirming Fe/S pathway defect\",\n      \"pmids\": [\"24281368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The pathogenic P144L mutation in FDX2 negatively affects the FDXR-dependent electron transfer pathway from NADPH to FDX2, reducing FDX2's capacity to assemble both [2Fe-2S] and [4Fe-4S] clusters. The C-terminal tail of FDX2 plays a functional role in electron transfer between FDX2 and FDXR. The P144L substitution alters protein-protein recognition between FDX2 and FDXR without perturbing the [2Fe-2S] cluster or overall protein structure.\",\n      \"method\": \"NMR structural and dynamic analysis of WT vs. P144L FDX2; in vitro electron transfer assays with FDXR; protein-protein interaction mapping\",\n      \"journal\": \"Protein science : a publication of the Protein Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal biophysical methods (NMR, in vitro electron transfer) with direct functional validation of mutant\",\n      \"pmids\": [\"39467201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FDX2 and frataxin compete for occupancy at the same binding site on NFS1 (cysteine desulfurase). Excess FDX2 inhibits frataxin-stimulated NFS1 activity in vitro and blocks Fe/S cluster synthesis in mammalian cell culture. Dominant suppressor mutations at the FDX2-NFS1 binding interface boost Fe/S cluster levels in the absence of frataxin, and partial knockdown of FDX2 ameliorates frataxin-deficient phenotypes.\",\n      \"method\": \"Genome-scale forward genetic screen in C. elegans; in vitro NFS1 activity assays with FDX2 titration; mammalian cell culture Fe/S cluster synthesis assays; mouse model of Friedreich's ataxia with FDX2 heterozygous reduction\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic screen validated by in vitro biochemistry and mammalian cell and mouse model experiments, multiple orthogonal approaches\",\n      \"pmids\": [\"41372402\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Conditional knockout of FDX2 in ovarian cancer cells causes global downregulation of Fe/S-containing proteins and Fe2+ overload, leading to DNA damage and p53 pathway activation. Depending on p53 status and phospholipid homeostasis, FDX2 loss drives either cellular senescence, apoptosis, or ferroptosis.\",\n      \"method\": \"Conditional knockout cell line; western blot for Fe/S proteins; Fe2+ measurement; DNA damage markers; p53 pathway analysis; ferroptosis sensitivity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean conditional KO with multiple pathway readouts in single lab study\",\n      \"pmids\": [\"39151727\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A novel splicing mutation in FDX2 (c.200+4 A>G) generates a mutant protein with 19 N-terminal residues replaced by 21 different amino acids; patient cells have low FDX2 levels, impaired mitochondrial respiration, defects in Fe/S proteins, enhanced mitochondrial iron accumulation, and diminished mitochondrial SOD2 levels.\",\n      \"method\": \"Patient fibroblast analysis; NMR structural comparison of mutant vs. WT FDX2; mitochondrial respiration assays; Fe/S protein activity measurements; iron quantification\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient-derived cells with multiple biochemical readouts and structural characterization of mutant protein\",\n      \"pmids\": [\"41372147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Paramagnetic NMR and DFT calculations reveal that the [Fe2S2]2+ cluster of FDX2 has inequivalent iron centers, with electron spin density transfer between inorganic sulfide ions and aliphatic carbon atoms via C-H---S-Fe3+ interactions; the magnetic exchange coupling constant between the two Fe3+ ions is ~386 cm-1.\",\n      \"method\": \"Paramagnetic NMR spectroscopy with complete assignment of binding-loop residues; density functional theory quantum chemical calculations\",\n      \"journal\": \"Inorganic chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — structural/electronic characterization by NMR and DFT in single study without functional mutagenesis validation\",\n      \"pmids\": [\"40121555\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FDX2 is a mitochondrial [2Fe-2S] ferredoxin that receives electrons from NADPH via FDXR and donates them specifically to the Fe/S cluster assembly machinery: it reduces the NFS1/ISD11/ACP cysteine desulfurase complex to drive [2Fe-2S] cluster synthesis on ISCU2, and subsequently catalyzes reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 (with IBA57) to form [4Fe-4S] clusters for mitochondrial [4Fe-4S] apoproteins; FDX2 and frataxin compete for the same site on NFS1, such that their stoichiometric balance regulates Fe/S cluster output, and FDX2's distinct substrate specificity (versus FDX1's role in steroidogenesis/heme a/lipoylation) is encoded by small conserved sequence motifs.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FDX2 is a mitochondrial [2Fe-2S] ferredoxin dedicated to iron-sulfur cluster biogenesis. It accepts electrons from NADPH via ferredoxin reductase FDXR and donates them to the NFS1/ISD11/ACP cysteine desulfurase complex to drive [2Fe-2S] cluster assembly on ISCU2, and subsequently catalyzes reductive [2Fe-2S] cluster fusion on the ISCA1-ISCA2 scaffold (with IBA57) to generate [4Fe-4S] clusters for mitochondrial apoproteins; its paralog FDX1 cannot substitute in these reactions, and the distinct substrate specificity is encoded by small conserved sequence motifs [PMID:20547883, PMID:32817474, PMID:36280795]. FDX2 and frataxin compete for the same binding site on NFS1, and their stoichiometric balance governs Fe/S cluster output such that excess FDX2 inhibits frataxin-stimulated desulfurase activity and partial FDX2 reduction ameliorates frataxin-deficient phenotypes [PMID:41372402]. Loss-of-function mutations in FDX2 cause a mitochondrial disorder with impaired respiratory chain complex activities, mitochondrial iron accumulation, and myopathy [PMID:24281368, PMID:41372147].\",\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"The first functional dichotomy between the two human ferredoxins was established: FDX2 is essential for Fe/S cluster and heme A biosynthesis while FDX1 is specific for steroidogenesis, resolving a long-standing question about why mammals retain two mitochondrial ferredoxins.\",\n      \"evidence\": \"RNAi depletion of FDX1 and FDX2 in human cells with measurement of multiple mitochondrial pathways\",\n      \"pmids\": [\"20547883\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No reconstituted biochemical system to show direct electron transfer to Fe/S assembly machinery\",\n        \"Heme A involvement of FDX2 was later reassigned to FDX1\",\n        \"Molecular basis of substrate selectivity between the two paralogs unknown\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A human loss-of-function mutation confirmed FDX2's physiological essentiality for Fe/S-dependent mitochondrial enzymes and established FDX2 deficiency as a cause of mitochondrial disease.\",\n      \"evidence\": \"Exome sequencing identifying c.1A>T start-codon mutation; respiratory chain enzyme assays in patient muscle\",\n      \"pmids\": [\"24281368\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single family; no rescue experiment to confirm causality\",\n        \"Degree of residual FDX2 protein expression not quantified precisely\",\n        \"No structure-function insight from this mutation\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The physical interaction between FDX2 and the NFS1/ISD11/ACP cysteine desulfurase complex was mapped at atomic resolution, revealing that FDX2 binds more tightly than FDX1 and supports faster Fe/S cluster assembly on ISCU.\",\n      \"evidence\": \"NMR binding-interface mapping, isothermal titration calorimetry, and in vitro Fe/S cluster assembly on ISCU\",\n      \"pmids\": [\"28001042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Binding interface of FDX2 with downstream late-acting ISC components not characterized\",\n        \"Physiological relevance of the affinity difference between FDX1 and FDX2 for the desulfurase complex not tested in cells\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"FDX2 was shown to be uniquely required for the late step of [4Fe-4S] cluster maturation, catalyzing reductive [2Fe-2S] cluster fusion on the ISCA1-ISCA2 scaffold in an IBA57-dependent manner — a reaction no other cellular reductant could support.\",\n      \"evidence\": \"Full in vitro reconstitution of [4Fe-4S] aconitase maturation with all physiological ISC components\",\n      \"pmids\": [\"32817474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of FDX2 recognition by the ISCA1-ISCA2 scaffold not determined\",\n        \"Whether FDX2 transfers one or two electrons per fusion event unclear\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The molecular determinants encoding ferredoxin substrate specificity were identified: small conserved sequence motifs can transfer FDX2's Fe/S assembly role to FDX1 and vice versa, definitively separating the two paralogs' functions.\",\n      \"evidence\": \"Motif-swapping mutagenesis combined with RNAi knockdown and in vitro electron transfer assays\",\n      \"pmids\": [\"36280795\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Crystal or cryo-EM structure of the FDX2–target complex showing how these motifs mediate recognition unavailable\",\n        \"Whether the motifs affect binding affinity, electron transfer rate, or both was not quantitatively dissected\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The pathogenic P144L mutation was shown to impair FDXR-dependent electron delivery to FDX2 by disrupting protein-protein recognition at FDX2's C-terminal tail without perturbing the [2Fe-2S] cluster, revealing a functional role for the C-terminus in the electron transfer relay.\",\n      \"evidence\": \"NMR structural/dynamic comparison of WT vs. P144L FDX2; in vitro electron transfer assays with FDXR\",\n      \"pmids\": [\"39467201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Quantitative impact of P144L on in-cell Fe/S cluster levels not measured\",\n        \"Whether other disease mutations similarly target the FDXR interface unknown\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Conditional FDX2 knockout in cancer cells revealed that global Fe/S protein loss triggers Fe²⁺ overload, DNA damage, and p53 activation, with cell fate (senescence, apoptosis, or ferroptosis) determined by p53 status and lipid homeostasis.\",\n      \"evidence\": \"Conditional KO in ovarian cancer cells; Fe²⁺ quantification; DNA damage markers; ferroptosis sensitivity assays\",\n      \"pmids\": [\"39151727\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single cancer cell type; generalizability to other tissues not established\",\n        \"Whether ferroptosis sensitivity is a direct consequence of Fe/S loss or secondary iron overload not distinguished\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A forward genetic screen uncovered that FDX2 and frataxin compete for the same binding site on NFS1, establishing that their stoichiometric balance directly regulates Fe/S cluster output and providing a mechanistic basis for therapeutic reduction of FDX2 in Friedreich's ataxia.\",\n      \"evidence\": \"Genome-scale C. elegans screen; in vitro NFS1 activity titrations; mammalian cell Fe/S assays; mouse Friedreich's ataxia model with FDX2 heterozygous reduction\",\n      \"pmids\": [\"41372402\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of competitive binding at the shared NFS1 site not resolved at atomic level\",\n        \"Long-term safety and efficacy of FDX2 reduction in mammalian Friedreich's ataxia models not determined\",\n        \"Whether FDX2-frataxin competition is regulated by post-translational modifications unknown\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Paramagnetic NMR combined with DFT calculations resolved the electronic structure of FDX2's [2Fe-2S]²⁺ cluster, revealing inequivalent iron centers and spin-density transfer through C-H···S-Fe³⁺ interactions.\",\n      \"evidence\": \"Paramagnetic NMR with full binding-loop assignment; DFT quantum chemical calculations\",\n      \"pmids\": [\"40121555\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No functional mutagenesis to test how perturbing these electronic features affects electron transfer\",\n        \"Whether these electronic properties differ between FDX2 and FDX1 and account for specificity not examined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the atomic-resolution structure of FDX2 in complex with NFS1 or ISCA1-ISCA2, the mechanism by which FDX2-frataxin competition is physiologically regulated, and whether FDX2 reduction is a viable therapeutic strategy for Friedreich's ataxia in long-term preclinical models.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of FDX2 bound to any of its physiological partner complexes\",\n        \"Regulatory mechanisms controlling FDX2 expression or stability in response to Fe/S demand unknown\",\n        \"Therapeutic window for FDX2 reduction in Friedreich's ataxia not defined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 2, 4, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [4, 5, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"FDXR\",\n      \"NFS1\",\n      \"ISCU\",\n      \"ISCA1\",\n      \"ISCA2\",\n      \"IBA57\",\n      \"FXN\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}